module CF where

import Util

import Control.Monad

-- the type of context-free grammars is parametrized
-- over the type categories and the type of tokens
data CF a b = CF { start :: a, 
		   nrules :: Table a [NRule a], 
		   trules :: Table b [TRule a b] }
	deriving (Eq,Ord,Show)

type NRule a = (a,[a])
type TRule a b = (b,a)

(|>) :: a -> [a] -> NRule a
(|>) = (,)

(|:) :: b -> a -> TRule a b
(|:) = (,)

mkCF :: (Ord a, Ord b) => a -> [NRule a] -> [TRule a b] -> CF a b
mkCF s nrs trs = CF { start = s, 
		      nrules = mkTableBy fst nrs,
		      trules = mkTableBy fst trs }

rhss :: Eq a => CF a b -> a -> [[a]]
rhss cf c = map snd $ lookupList c (nrules cf)

tokenCats :: Eq b => CF a b -> b -> [a]
tokenCats cf x = map snd $ lookupList x (trules cf)

allNRules :: CF a b -> [NRule a]
allNRules = concatMap snd . nrules